1. Field of the Invention
This invention relates to an anatomical characteristic position detecting system and an object structure measurement system for aiding in diagnosing anatomical structure of an object on the basis of a medical image.
2. Description of the Related Art
It has been carried out to measure a structural part such as a bone or an organ by the use of a medical image. For example, when diagnosing cardiomegaly, the widths of the thorax and the heart are measured by the use of a chest radiation image and the ratio of the latter to the former (cardiothoracic ratio) is calculated.
Conventionally, the widths of the thorax and the heart have been manually measured by applying a scale to the chest radiation image. Recently, an image is often digitized and handled as digital image data, and there is a demand for automatically calculating the cardiothoracic ratio on the basis of the digital image data.
In order to meet this demand, there have been proposed various technologies of automatically calculating the cardiothoracic ratio. To calculate the cardiothoracic ratio, it is necessary to identify the profiles of the thorax and the heart (cardiothorax). As the method of detecting the profile of the cardiothorax, there have been known a method disclosed in U.S. Pat. Nos. 5,790,690 and 6,011,862 where the profile of the thorax (a region including the left and right lungs), which is a closed region, is detected and a method proposed by Mr. Katsuragawa where the profile of the heart is detected by the use of a deformation ellipse model function. Further, there has been proposed in U.S. Laid-Open No. 20020057828 a method where the image of the chest is expressed in a polar coordinate system, the profile of the cardiothorax is automatically detected by template matching on the plane of the polar coordinate system by the use of a template which is substantially similar to the average cardiothorax profile (a reference profile), and the cardiothoracic ratio is calculated on the basis of the automatically detected profile of the cardiothorax.
However, it has been found that by the method disclosed in U.S. Laid-Open No. 20020057828, the error of the detected cardiothorax profile from the actual profile is too large to obtain an accuracy necessary to diagnosis. Accordingly, this applicant has proposed in Japanese Unexamined Patent Publication No. 2003-6661 a more accurate method where the cardiothorax profile is divided into a plurality of regions and the regions are recombined after edges on borders of regions are detected.
However, the method disclosed in Japanese Unexamined Patent Publication No. 2003-6661 is disadvantageous in that edges on borders cannot be accurately found when fat is on the heart due to heart disease or edges are not clear due to noise.